1. Field of the Invention
The present invention relates generally to rocket engines, and in particular to rocket engines that include an expansion-deflection nozzle.
2. Discussion of the Related Art
A typical liquid-fueled rocket engine includes a cylindrically symmetric combustion chamber that has an injector attached to one end and a flared nozzle attached to an opposing end. A liquid propellant including fuel and oxidizer flows through injector ports in the injector and into the combustion chamber. The propellant is ignited within the combustion chamber, causing a rapid expansion in combustion gases which are emitted through the nozzle. The rapidly exiting gases drive the rocket engine and attached rocket structure in the opposite direction.
The nozzle serves to transform the energy produced in the combustion chamber into a driving force by transforming the potential energy contained in the combustion gases into kinetic energy provided by the pressure-reduced exiting gases. In an ambient vacuum environment, the efficiency of the transformation process improves as the pressure drop provided by the nozzle increases. Conventional conical or Bell expansion nozzles used on rocket engines suffer from performance inefficiencies when operated at variable altitudes during flight, due to variable nozzle ambient backpressure. The inefficiencies occur because the typical nozzle can only be optimized for maximum nozzle thrust coefficient at one backpressure condition. Since the maximum nozzle thrust coefficient varies with altitude, the thrust developed by the rocket engine also varies with altitude.
Therefore, there is a need for a nozzle that is self-compensating in response to variable external pressures so that expansion efficiency, and therefore thrust, is maximized regardless of the range of operating altitudes the rocket may experience. Conventional expansion-deflection, or plug, nozzles have been known to provide self-compensation for varying ambient backpressures. However, conventional plug nozzles have been limited due to thermal management problems with the plug immersed in the exhaust flow and the associated support structure. Universally, conventional nozzle plugs do not attach to the propellant injector due to the excessive temperatures that exist within the vicinity of the injector. Instead, the nozzle plug is attached to a wall of the combustion chamber or nozzle throat. Heretofore, using a conventional nozzle plug with internal expansion off of the plug has not been practical due to severe thermal loads imposed on support structures associated with the plug. To operate correctly, the plug must be mechanically supported within the flow of the combustion gases. However, heat generated by the combustion gases and gas flow velocities approaching Mach 1 at the nozzle throat impose intense thermal loads on the support structures.
The present invention provides a rocket engine that is self-compensating for varying ambient backpressures. The rocket engine includes a combustion chamber having an injector end and a nozzle end. A propellant injector is in fluid communication between one or more propellant lines and an inside periphery of the combustion chamber at the injector end. A nozzle throat is formed at the nozzle end of the combustion chamber. A nozzle exit cone extends outwardly from the nozzle throat. A plug support is coupled between a nozzle plug and the injector. The nozzle plug aerodynamically self-compensates for changes in ambient backpressure at the nozzle exit cone such that the nozzle thrust coefficient is maximized for any ambient backpressure.
For a more complete understanding of the invention, its objects and advantages, reference may be had to the following specification and to the accompanying drawings.